Mass produced clock operated thermostats are normally installed in a variety of different types of heating and cooling applications. The same basic thermostat may be used for control of a forced air heating and cooling system, all electric systems, normal hydronic systems, and oversized hydronic systems. Each of these types of installations have entirely different characteristics in response to a normal setup, or setback, that is accomplished for energy savings by a clock thermostat.
While attempts has been made to provide adjustments in the cycling rate of a thermostat for a particular type of heating plant, this type of accommodation normally will not provide good comfort control when the thermostat calls for a sudden setup in temperature that has been programmed into the thermostat. Typically, a substantial morning pickup is provided by clock operated thermostats. The space temperature is normally controlled at a relatively low temperature during the night to save energy. In the morning a setup occurs in order to move the space temperature from the lower energy saving level to a desired higher comfort level. This typically locks the heating plant into a full "on" state, and the space temperature rises at a rate that is a function of the particular parameters of the heating plant and the environment in which it is used. This arrangement can cause substantial overshoot of the space temperature compared to the setpoint temperature that is being called for by the clock thermostat. Ordinarily, in an hour or two, this overshoot corrects itself, but it is an undesirable result of the sudden setpoint change that occurs when pickup is programmed into this type of thermostat.